Temozolomide, a new alkylating agent, is a second generation imidazotetrazine which has a broad spectrum of activity against murine tumor models. It appears to be well tolerated by humans. This phase I trial seeks to determine the maximum tolerable dose of oral temozolomide given daily for 5 days; to determine the toxicities of temozolomide given on this schedule; to determine the anti-tumor activity within the confines of a phase I study; and to determine the PK behavior of temozolomide when administered orally for five consecutive days.